The basic shape, dimensions, and method of manufacture of aerosol metal containers and their companion mounting cups have become relatively standardized. Typically, the containers are made of tin plated steel or aluminum and are provided at one end with an opening which is circumscribed by an annular rounded bead. The peripheral rim of the mounting cup is crimped to the annular rounded bead joining the two parts together.
Aluminum containers are generally formed by common metal forming processes such as extrusion or cold drawing. In these processes, a flat piece of metal is formed into a hollow cylindrical body. The cylinder has a flat closed base on one end and an opening on the other end. The open end of the cylinder undergoes forming operations until the desired neck and opening dimensions are reached. The edges of the container defining the opening are then curled over to form the rounded bead, similar to a hollow annular shoulder.
Conventional mounting cups have a peripheral rim which is capable of being crimped to the annular rounded bead located on the aerosol container. Often, a plastic or rubber material, such as a gasket, is interposed between the mounting cup and the metal aerosol container for ensuring a proper seal.
With known mounting cups for metal containers, the Peripheral rim is formed in a substantially inverted U-shape so as to correspond to the shape of the curled end of the container as nearly as possible, the underlying theory being that such a shape will promote sealing between the mounting cup and the container. The peripheral rim of the mounting cup is placed upon the annular rounded bead of the container with the gasket material disposed therebetween. The mounting cup is then crimped by an expanding collet to urge the peripheral rim into sealing engagement with the annular rounded bead of the container.
As a consequence of the forming operation for aluminum container bodies, grooves known as eyelashes develop longitudinally along the internal surface of the container. Depending upon the dimensions of the groove and the physical characteristics of the contents of the container, the solution and/or propellant in the container may escape from the container along the grooves. Accordingly, it has become necessary to improve the seal between the mounting cup and the aerosol container.
Numerous sealing methods and devices have been proposed for improving the seal between the peripheral rim of the mounting cup and the container body. Generally, these improvements involving interposing a sealing material between the annular rounded bead and the mounting cup rim. Other attempts to improve the seal between the mounting cup and the container body include utilizing mounting cups and container bodies formed from a metallic sheet material which had been precoated or laminated with a plastic sealing material. The laminated surface is thought to provide a better seal when the mounting cup is secured or crimped to the container body.
The shape of the mounting cup has been relatively untouched in the search for a better sealing container assembly. The controlling belief has been that an effective seal is obtained by forming the peripheral rim of the mounting cup in a shape matching as similarly as possible to the shape of the annular rounded bead of the metal container.
In U.S. Pat. No. 4,813,576, the shape of the mounting cup rim prior to mounting was modified so as to be different from the shape of the associated metal container bead. However, once attached to the container, the shape of the peripheral rim of the mounting cup closely mirrored the rounded shape of the annular bead. In plastic aerosol containers, mounting cups with rectilinear rims have been used. However, in these embodiments the annular bead is also rectilinearly shaped.